Unmottled dye transfer



United States Patent Ofiice 3,003,891 UNMOTTLED DYE TRANSFER Howard W. Albrecht, Columbus, Ohio, assignor, by mesne assignments, to Xerox Corporation, Rochester, N.Y., a corporation of New York No Drawing. Filed Nov. 19, 1958, Ser. No. 774,847 4 Claims. (@131. 117-175) This invention relates to xerography and more particularly to the transfer of Xerographic dye images.

In a usual form of xerography, an electrostatic latent image is formed on the normally insulating surface of a xerographic plate and this charge pattern is then made visible by selective deposition thereon of finely divided electrostatically attractable powder particles. These particles commonly comprise finely divided particles of pigmented synthetic resins, finely divided carbon, minerals, pigments, etc. The powder image is then customarily transferred to another support, such as a sheet of paper, for examination. In another form of Xerography with which the present application is concerned, electrostatic charge patterns are developed or made visible by the deposition of finely divided particles of water soluble dyes. The development operation, which is not itself a part of the present invention, may be carried out in a number of ways, such as through cascade development, aerosol de-.

velopment, or the like, and results in a dry dye image deposit on the charge pattern bearing surface. Various forms of normally insulating layers are known for use in Xerographic plates, including, but not limited to, vitreous materials, such as vitreous selenium, as well as dispersions of photoconductive pigments in insulating resin binders. In substantially every case, and in every case in which this invention is applicable, the normally insulating layer which carries the electrostatic charge pattern and which is developed by the dye particles is, in a practical sense, insoluble in and impermeable to water.

It has been customary to transfer such xerographic dye images to an image support comprising a layer of hardened gelatin generally containing a mordant and coated upon a suitable mechanical support base. The hardened gelatin layer may be replaced by other slightly water permeable materials having similar physical properties, such as other natural or synthetic colloids. This type of material is preferred because of the density and intensity of dye images attainable thereon as compared with other possible materials, such as ordinary paper. v A suitable commercial product of this type is available from the Eastman Kodak Company, Rochester, New York, under the name dye transfer paper and generally comprises a sheet of white paper coated with a layer of hardened gelatin containing a mordant. The image receiving member will be referred to throughout this specification as dye transfer paper without any intent to be limited to a particular commercial product.

The transfer of the dye image has generally been effected by soaking a sheet of dye transfer paper in water for several minutes and then partially drying the sheet by passing it through a pair of wringer rollers while sandwiched between two sheets of blotting paper or optionally between a sheet of blotting paper and a polished metal plate. This technique of preparing the dye transfer paper is fully disclosed in US. Patent 2,843,499. The sheet of dye transfer paper which is now in a damp condition, is then placed against the xerographic plate, with its gelatin surface contacting the dye image. After a short interval of several minutes, the dye transfer paper may be removed and a brilliant dye image is found to be imbibed into the gelatin layer. This transfer procedure, however, is incapable of producing high quality dye images because the denser parts of the image are invariably found to be badly mottled after transfer. It is presently believed that this mottling is due to the liberation of a small amount of free water at the surface of the dye transfer paper where it is pressed into contact with the Xerographic plate, thus forming a concentrated solution of the dye which is randomly displaced before it is absorbed into the gelatin. It is also believed that in the less dense portions of the image the lesser amounts of dye are immediately absorbed by the dye transfer paper before mottling can take place. It has also been proposed that the dye cannot be diffused into the hardened gelatin surface as fast as it is solubilized and consequently that the dye is squeezed into the small, irregularly spaced indentations on the surface of the paper to give a mottled appearance. It has been found that if the moisture content of the dyetransfer paper is reduced in an attempt to avoid mottle, incomplete transfer results. Regardless of the validity of the proposed theoretical explanations, it has not heretofore been possible to transfer onto dye transfer paper Xerographic dye images without mottle and having both high quality and high density.

In accordance with the present invention, however, the Xerographic plate with its associated dye deposit is first contacted with a dampened layer or member which is highly permeable to water, unlike dye transfer paper which is only slightly permeable. elude, but are not limited to, fibrous materials such as paper, soft colloids such as unhardened gelatin, and dispersions of finely divided pigments in water permeable binders. When the xerographic plate is contacted by such a layer the dye thereon is almost immediately imbibed stantial portion of the dye image will have been imbibed into the gelatin layer of the dye transfer paper forming thereon an unmottled reproduction of the original dye" image on the Xerographic plate.

While a large number of materials may be used as the intermediate transfer layer in carrying out this invention, it is apparent that attainment of the highest quality results in dependence upon the particular material chosen. Thus, the material-must be quite water absorbent and water permeable in order to rapidly remove the dye image from the xerographic plate; it must not be too permeable in order to minimize diffusion of the dye with attendant loss of image resolution; and finally it must surrender most of the dye back to dye transfer paper in order to achieve a dense image. A particularly suitable material for this purpose is so-called baryta coated paper. This is a commercial product which is supplied by papermakers to manufacturers of photographic enlarging paper or the like who use it as a base upon which to coat silver halide photographic emulsions. It comprises a high grade of paper upon which is coated a thin layer of barium sulphate in a gelatinous binder. It is sometimes supplied with a textured or embossed surface, but a smooth surface is obviously preferred for the present application.

In use, the baryta paper is soaked in water, partially dried by the method already described for use with dye Patented Oct. 1 0, 1 9 61 Suitable materials in-' sheet of dye transfer paper which has been moistened by the same previously described procedure. The dye transfer paper including a gelatin layer that swells and softens but does not dissolve when moistened and is in a substantially non-tacky condition while damp comprises a chemically hardened gelatin layer overlying a support base and as is more fully described in the aforementioned reference US. Patent 2,843,499, the gelatin layer may be prepared by adding to a 5% gel solution saponin to act as a spreading agent and formaldehyde which acts as the hardening agent. The dye transfer material is so soaked in water and then blotted to put it in a damp condition. It is then placed into contact with the baryta paper bearing the dye image. An approximately 5-minute period of contact is sufficient and results in nearly all of the dye migrating from the baryta paper to the dye transfer paper. There is thus formed on the dye transfer paper a brilliant, dense, and faithful reproduction of the original dye image. Transfer times less or greater than 5 minutes may be required, depending on such factors as temperature, water content of the dye transfer and baryta papers, and the diffusability of the dye. It is sometimes desirable to maintain a light pressure between the dye transfer and baryta papers while they are in contact to prevent the appearance of isolated small white spots in the finished image due to localized failure of the dye to transfer. Pressures ranging up to about 25 pounds per square inch are effective in preventing blemishes, but hi her pressures should generally be avoided since they may cause the baryta paper to adhere tenaciously to the dye transfer paper. Since the transfer procedure, according to the present invention, produces an image which is a direct reproduction of the original Xerographic dye image, whereas the prior art method produced a mirror reversed image, steps known to the art should be taken to cause the original Xerographic image to be mirror reversed from that used in the prior art processes.

Xerographically formed dye images are particularly useful in the reproduction of full color images and the present invention is particularly useful for that purpose. in one form of color xerography, according to the prior art, separate cyan, yellow, and magenta dye images are xerographically formed, either on separate xerographic plates or successively on a single plate. Each dye image is then separately transferred in register to a single sheet of dye transfer paper. In accordance with the present invention, mottle can be eliminated from the final image by first transferring each dye image to a separate sheet of baryta paper and then separately transferring the dye image in register from each sheet of baryta onto a single sheet of dye transfer paper. It is obvious, however, that in addition to the disadvantage of the mottled efiect which characterized the prior art transfer process, approximately 5 minutes are required in the prior art process for each individual transfer, giving a total time requirement of at least about minutes to prepare a single image. This time also can be shortened through the employment of the present invention by sequentially transferring each original dye image in register to a single sheet of baryta transfer and then transferring the three registered images to a single sheet of dye transfer paper in a single transfer step which only requires about 5 minutes. As has been noted, it requires only a very short time to transfer a dye image to baryta paper or to other highly absorbent material.

In addition to eliminating mottle and shortening the time required to transfer full color xerographic dye images, the present invention has a further advantage in reducing damage to Xerographic plates otherwise caused by transferring dye images. It has been found that when a dye solution is allowed to remain in contact with the plate for several minutes some form of deposit is left on the surface of the plate which cannot be washed off, and which impairs the reusability otherwise characteristic of xerographic plates. Where dye transfer paper is used directly against the Xerographic plate, the plate is necessarily contacted by the dye solution for the approximately 5 minutes required to eifect transfer. With the present invention, however, the plate is only contacted by the moistened baryta paper for a few moments and can then be washed off before the dye solution has had time to harm the plate.

Although the present invention has heretofore been described in terms of its utility for transferring Xerographically prepared dye images, it is apparent that it is equally useful for transferring dye images, however formed, from any water impermeable surface regardless of the electrical properties of that surface.

What is claimed is:

1. A method of transferring a water soluble dye image pattern of powder particles from a water impermeable surface of a Xerographic plate to a chemically hardened gelatin layer overlying a support base comprising rapidly absorbing the dye image into a first transfer member comprising a damp and highly absorbent smooth surfaced paper layer by placing said absorbent layer in a damp condition with the smooth surface thereof across the dye image, removing said first transfer member with the dye image imbibed therein away from the xerographic plate, and then slowly diffusing the dye image from the absorbent layer into a second transfer member comprising a chemically hardened gelatin layer overlying a support base by placing the chemically hardened gelatin layer in a damp condition against the dye carrying absorbent layer.

2. The method according to claim 1 in which the first transfer member comprises baryta paper.

3. The method according to claim 2 in which the second transfer member is pressed against the first transfer member for diffusion with a pressure of up to about 25 pounds per square inch.

4. The method of transferring multiple water soluble dye image patterns of powder particles from water impermeable surfaces of xerographic plates to a chemically hardened gelatin layer overlying a support base comprising rapidly absorbing each dye image in turn into a first transfer member comprising a single damp and highly absorbent smooth surfaced paper layer by placing said absorbent layer in a damp condition with the smooth surface thereof across each dye image and then removing said first transfer member with the dye image imbibed therein away from each Xerographic plate, and then slowly diffusing the combined dye image from the absorbent layer into a second transfer member comprising a chemically hardened gelatin layer overlying a support base by placing the said gelatin layer in a damp condition against the dye carrying absorbent layer.

References Cited in the file of this patent UNITED STATES PATENTS 1,528,660 De Sperati Mar. 3, 1925 2,761,416 Carlson Sept. 4, 1956 2,843,499 Andrus July 15, 1958 

1. A METHOD OF TRANSFERRING A WATER SOLUBLE DYE IMAGE PATTERN OF POWDER PARTICLES FROM A WATER IMPERMEABLE SURFACE OF A XEROGRAPHIC PLATE TO A CHEMICALLY HARDENED GELATIN LAYER OVERLYING A SUPPORT BASE COMPRISING RAPIDLY ABSORBING THE DYE IMAGE INTO A FIRST TRANSFER MEMBER COMPRISING A DAMP AND HIGHLY ABSORBENT SMOOTH SURFACED PAPER LAYER BY PLACING SAID ABSORBENT LAYER IN A DAMP CONDITION WITH THE SMOOTH SURFACE THEREOF ACROSS THE DYE IMAGE, REMOVING SAID FIRST TRANSFER MEMBER WITH THE DYE IMAGE IMBIBED THEREIN AWAY FROM THE XEROGRAPHIC PALTE, AND THEN SLOWLY DIFUSING THE DYE IMAGE FROM THE ABSORBENT LAYER INTO A SECOND TRANSFER MEMBER COMPRISING A CHEMICALLY HARDENED GELATIN LAYER OVERLYING A SUPPORT BASE BY PLACING THE CHEMICALLY HARDENED GELATIN LAYER IN A DAMP CONDITION AGAINST THE DYE CARRYING ABSORBENT LAYER. 